The present invention relates to a copier, printer, facsimile transceiver or similar equipment for copying or printing an image by an electrophotographic process and, more particularly, to an electrophotographic process control device capable of controlling an electrophotographic process on a step basis.
Generally, a photoconductive element, typically in the form of a drum, is used to implement an electrophotographic process and has characteristics relating to charging and exposure which are extremely susceptible to various factors and change in a complicated way, as well known in the art. The factors affecting such characteristics of the drum may generally be classified into three kinds, i.e., long-term deterioration factors including the wear and electrostatic fatigue of the drum, short-term deterioration factors including the fatigue of the drum due to exposure and the duration of suspension, and real-time deterioration factors including temperature variation. An optimal control method over the charge potential and amount of charge of the drum depends on the kind of the deterioration factors. It has been customary, however, to prepare a look-up table listing adequate control values in relation to the outputs of a surface electrometer and photosensors by experiments and to simply control the individual parameters by referencing the look-up table.
The conventional look-up table scheme has various problems left unsolved, as follows. To begin with, a look-up table is not attainable without resorting to a prohibitive amount of experiments. Since the control needs a huge amount of data and, moreover, it is effected without specifying the above-stated factors at all, the conventional control device is not applicable to a broad range and often causes the equipment to run out of control. Further, since the characteristics of various constituent parts of the equipment, e.g., grids and drum change or deteriorate due to the number of copies produced, temperature, humidity, toner concentration, fatigue of a developer, and so forth, a reproduction often suffers from contamination in the background thereof as well as from an irregular density distribution. Moreover, assume electrophotographic equipment of the type causing a charger to discharge in response to a grid voltage and dissipates part of the charge deposited on a photoconductive drum by a laser beam to thereby form a latent image. Then, it is likely that the surface potentials of the drum change due to, for example, the deterioration of the photoconductor thereof and charger, preventing a reproduction from having sufficient image density. Also, residual potentials are apt to rise in a continuous copy mode operation, contaminating the background of reproductions.